+Mark Rutland
Christopher Covington <c...@codeaurora.org> writes:
> Hi Larry,
>
> On 05/22/2014 03:27 PM, Larry Bassel wrote:
>> Make calls to ct_user_enter when the kernel is exited
>> and ct_user_exit when the kernel is entered (in el0_da,
>> el0_ia, el0_svc, el0_irq and all of the "error" paths).
>>
>> These macros expand to function calls which will only work
>> properly if el0_sync and related code has been rearranged
>> (in a previous patch of this series).
>>
>> The calls to ct_user_exit are made after hw debugging has been
>> enabled (enable_dbg_and_irq).
>>
>> The call to ct_user_enter is made at the beginning of the
>> kernel_exit macro.
>>
>> This patch is based on earlier work by Kevin Hilman.
>> Save/restore optimizations were also done by Kevin.
>
>> --- a/arch/arm64/kernel/entry.S
>> +++ b/arch/arm64/kernel/entry.S
>> @@ -30,6 +30,44 @@
>> #include <asm/unistd32.h>
>>
>> /*
>> + * Context tracking subsystem. Used to instrument transitions
>> + * between user and kernel mode.
>> + */
>> + .macro ct_user_exit, restore = 0
>> +#ifdef CONFIG_CONTEXT_TRACKING
>> + bl context_tracking_user_exit
>> + .if \restore == 1
>> + /*
>> + * Save/restore needed during syscalls. Restore syscall arguments from
>> + * the values already saved on stack during kernel_entry.
>> + */
>> + ldp x0, x1, [sp]
>> + ldp x2, x3, [sp, #S_X2]
>> + ldp x4, x5, [sp, #S_X4]
>> + ldp x6, x7, [sp, #S_X6]
>> + .endif
>> +#endif
>> + .endm
>> +
>> + .macro ct_user_enter, save = 0
>> +#ifdef CONFIG_CONTEXT_TRACKING
>> + .if \save == 1
>> + /*
>> + * Save/restore only needed on syscall fastpath, which uses
>> + * x0-x2.
>> + */
>> + push x2, x3
>
> Why is x3 saved?
I'll respond here since I worked with Larry on the context save/restore
part.
[insert rather embarassing disclamer of ignorance of arm64 assembly]
Based on my reading of the code, I figured only x0-x2 needed to be
saved. However, based on some experiments with intentionally clobbering
the registers[1] (as suggested by Mark Rutland) in order to make sure
we're saving/restoring the right things, I discovered x3 was needed too
(I missed updating the comment to mention x0-x3.)
Maybe Will/Catalin/Mark R. can shed some light here?
Kevin
[1]
>From 8a8702b4d597d08def22221368beae5db2f4a8aa Mon Sep 17 00:00:00 2001
From: Kevin Hilman <khil...@linaro.org>
Date: Fri, 9 May 2014 13:37:43 -0700
Subject: [PATCH] KJH: test: clobber regs
---
arch/arm64/kernel/entry.S | 38 ++++++++++++++++++++++++++++++++++++++
1 file changed, 38 insertions(+)
diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index 520da4c02ece..232f0200e88d 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -36,6 +36,25 @@
.macro ct_user_exit, restore = 0
#ifdef CONFIG_CONTEXT_TRACKING
bl context_tracking_user_exit
+ movz x0, #0xff, lsl #48
+ movz x1, #0xff, lsl #48
+ movz x2, #0xff, lsl #48
+ movz x3, #0xff, lsl #48
+ movz x4, #0xff, lsl #48
+ movz x5, #0xff, lsl #48
+ movz x6, #0xff, lsl #48
+ movz x7, #0xff, lsl #48
+ movz x8, #0xff, lsl #48
+ movz x9, #0xff, lsl #48
+ movz x10, #0xff, lsl #48
+ movz x11, #0xff, lsl #48
+ movz x12, #0xff, lsl #48
+ movz x13, #0xff, lsl #48
+ movz x14, #0xff, lsl #48
+ movz x15, #0xff, lsl #48
+ movz x16, #0xff, lsl #48
+ movz x17, #0xff, lsl #48
+ movz x18, #0xff, lsl #48
.if \restore == 1
/*
* Save/restore needed during syscalls. Restore syscall arguments from
@@ -60,6 +79,25 @@
push x0, x1
.endif
bl context_tracking_user_enter
+ movz x0, #0xff, lsl #48
+ movz x1, #0xff, lsl #48
+ movz x2, #0xff, lsl #48
+ movz x3, #0xff, lsl #48
+ movz x4, #0xff, lsl #48
+ movz x5, #0xff, lsl #48
+ movz x6, #0xff, lsl #48
+ movz x7, #0xff, lsl #48
+ movz x8, #0xff, lsl #48
+ movz x9, #0xff, lsl #48
+ movz x10, #0xff, lsl #48
+ movz x11, #0xff, lsl #48
+ movz x12, #0xff, lsl #48
+ movz x13, #0xff, lsl #48
+ movz x14, #0xff, lsl #48
+ movz x15, #0xff, lsl #48
+ movz x16, #0xff, lsl #48
+ movz x17, #0xff, lsl #48
+ movz x18, #0xff, lsl #48
.if \save == 1
pop x0, x1
pop x2, x3
--
1.9.2
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